1. Field of the Invention
The present invention relates generally to methods and apparatus for determining the test type to be performed on various types of test elements. More particularly, this invention provides methods for distinguishing between different types of test elements, including analytical test strips with fluid samples applied to them, analytical test strips with control solution applied to them, and standard strips as measured by a reflectance-type testing device.
2. Background of the Invention
Monitoring analytes such as glucose, cholesterol, intoxicants, and other constituents is frequently desirable in fluids, such as blood, plasma, blood serum, saliva, urine, and other biological fluids. In healthcare applications, such monitoring affords the opportunity to make rapid diagnoses of a patient""s condition and to take prophylactic or therapeutic measures necessary for maintaining proper health.
One such healthcare application that has benefited tremendously by analyte monitoring in recent years is the treatment of diabetes. Diabetics suffer from an impaired ability to regulate glucose levels in their blood. As a result, diabetics can have abnormally high blood sugar levels known as hyperglycemia. Chronic hyperglycemia may lead to long-term complications such as cardiovascular disease and degeneration of the kidneys, retinas, blood vessels and the nervous system. To minimize the risk of such long term complications, diabetics must strictly monitor and manage their blood glucose levels.
Diabetics that have glucose levels that fluctuate several times throughout the day require very close blood glucose level monitoring. Close monitoring of blood glucose levels is most easily obtained when a diabetic is able to monitor their glucose levels themselves. Many devices currently available allow diabetics to measure their own blood sugar levels.
Reflectance-based monitors comprise one category of personal, or home-use, glucose level monitoring devices. These monitors utilize an optical block which accepts test elements for photometric analysis.
The test elements are usually in the form of test strips, which contain analytical chemistry. Conventionally, these test strips are in the form of a disposable diagnostic test strip containing analytical chemistry upon which a fluid sample is deposited. Once the user applies the fluid sample to the test strip, and the sample has sufficiently penetrated the test strip, a chemical reaction occurs in the presence of a target analyte, e.g., glucose, to cause a change in the optical properties of the test strip. An optical photometric device then determines the analyte level of the sample by measuring an optical property, such as the intensity of reflected light at a certain wavelength from the test strip. For in vitro analysis in healthcare applications, the fluid sample is usually fresh whole blood. Periodically, however, it is desirable to run a test on a test element formed by applying a control solution of known analyte concentration to a test strip, in order to verify that the meter is performing within operational limits. It is also desirable for the user to insert a xe2x80x9cstandard stripxe2x80x9d, which is a test element that has known optical properties, in order to verify that the meter is operating within operational limits.
Diagnostic test strips for testing analytes such as glucose levels of blood samples are well known in the art and comprise various structures and materials. Test strips typically include single or multi-layered porous membrane arrangements which receive a blood sample and undergo a change in an optical property, such as a color change, in response to the interaction of blood glucose with agents/reactants in the membrane. Examples of such multi-layer strips are described in U.S. Pat. Nos. 5,296,192 to Carroll and 6,010,999 to Carroll et al., the contents of both of which are incorporated herein by reference.
Prior to reaching the reactants, a whole blood sample can be filtered to eliminate potential optical interference by removing erythrocytes, or red blood cells. Some test strips operate to allow the applied blood sample to migrate to a reaction site in the membrane where the sample reacts with the agents/reactants, which is located in downstream capillary relation to the sample application site. The results of the reaction are often visible as a color change at the reaction site. However, the change may occur in invisible regions of the electromagnetic spectrum, such as infrared and ultraviolet. For the purposes of this application, the term xe2x80x9ccolor changexe2x80x9d will be understood to include variations in optical properties throughout the visible and invisible regions of the electromagnetic spectrum. As noted above, a color change can be correlated to the amount of glucose in the sample. Home-use glucose measuring devices that use a reflectance meter to measure the color change of the test strip correlate glucose levels to the change in the amount of light reflected from the reaction site of the test strip. As is well known in the art, strips can be formulated to produce a color change within a certain spectral region, and the meter designed to photometrically measure reflected, absorbed or transmitted light at a wavelength sensitive to the color change of the strip. While the present invention will be described with reference to reflectance based photometry, it would be known to one having ordinary skill in the art to apply the features of the invention to absorbance or transmittance based systems.
Desirable for maintaining the accuracy of blood glucose monitoring devices is the periodic checking of the device to ensure that it is within operational compliance. As mentioned above, certain periodic standardization tests performed by the user provide verification of the meter""s accurate operation. Accuracy is required by regulatory authorities for medical devices such as diabetes testing monitors, where a patient""s life can depend on proper operation of the monitoring system.
Common verification techniques are designed to periodically check whether the monitoring device is operating properly, and thus accurately measuring blood glucose levels. Verification techniques used in glucose level monitoring devices include inserting test elements having a known glucose or reflectance value into the monitoring unit and comparing the measured results with the known values. Test elements having known glucose levels (xe2x80x9cControl Test Elementsxe2x80x9d hereinafter) are normally prepared by applying a glucose control solution having a known glucose concentration to a dry test strip that normally could be used to run a test with blood. The control test element is then inserted into the monitoring unit and a test is performed and the calculated glucose value of the test element is displayed. The calculated glucose value is then compared with a range of acceptable results provided by the manufacturer for the glucose control solution. If the results displayed by the device for the control test element fall with an acceptable range designated for the solution, the device is deemed to be appropriately functioning ready for testing a blood sample.
Another verification technique commonly used in glucose level monitoring devices includes inserting a strip with a known reflectance value into the monitoring unit (xe2x80x9cStandard Test Elementxe2x80x9d of xe2x80x9cStandard Stripxe2x80x9d hereinafter). This standard test element does not receive a fluid sample, but is rather formed of a one piece rigid or semi-rigid material such as plastic having known optical properties. The standard reflectance strip can be stored in a compartment of the monitoring unit so that it is conveniently available for use throughout the life of the monitoring device. The standard reflectance strip is inserted into and measured by the device just as other test strips, and the measurement results are compared with a range of acceptable results provided with standard reflectance strip. As with the test using the glucose control test element, if the results of the measurement fall within an acceptable range, the device is ready for testing a blood sample.
The test run with the standard test element (xe2x80x9cStandard Testxe2x80x9d hereinafter) is intended to test the performance of the monitoring device only, while the test run with the control test element (xe2x80x9cControl Testxe2x80x9d hereinafter) is intended to check the entire monitoring process including the testing technique of the user. Conventional glucose monitoring devices are capable of performing both types of calibration techniques and will normally include instructions regarding when to initiate each type of calibration technique.
Of course, the monitoring device must also accept a test element formed by sample fluid, such as blood, applied to a test strip (xe2x80x9cAnalytical Test Elementxe2x80x9d hereinafter), and run an analytical test thereon to determine analyte concentration (xe2x80x9cAnalytical Testxe2x80x9d hereinafter).
A problem with prior art devices has been that they have typically not been able to discriminate between the type of test element introduced into the meter, and therefore the type of test to run, without user intervention. For example, the standard test is instantaneous and need not ascertain that a reaction on a test strip has run to completion, as is required in the control test and the analytical test. It is also desirable that the historical results for all three tests should be stored separately, so that the user""s results from the analytical tests are not mixed in or displayed with the standard test or control test results.
Conventional methods for differentiating the test type have required the user to perform an affirmative act, such as pressing a button on the device, to signal to the device that the test strip inserted includes a glucose control solution and not a blood sample.
The requirement that a user perform an affirmative act to signal to the monitoring device the type of sample tested allows the possibility for human error that can adversely affect the proper storing and monitoring of measurement results, and possibly the misinterpretation of stored results. For example, if a user were to fail to perform a required step indicating insertion of a test strip containing glucose control solution, such as failing to push a button or wait a specified time, the measurement results could be incorrectly stored in the memory of the device as an actual blood glucose level result, possibly resulting in, among others, false self-diagnosis of blood sugar levels or erroneous treatment regimens being prescribed by healthcare professionals.
Another prior art system is a xe2x80x9cnegative bloodxe2x80x9d approach, which uses two wavelengths. In such a system, a secondary LED which measures at a wavelength at which red blood cells are highly detectable. This measurement is used to formulate a correction factor used in running the glucose test in whole blood to subtract out optical interference caused by hemoglobin. This arrangement is usually necessary in conjunction with single-layer test strips, which are generally unable to adequately separate hemoglobin from whole blood sample as it flows to the opposite surface where the colorimetric reaction with the reagent is desired to be measured. If reflection from this secondary LED is not detected to achieve a certain threshold, that is if there is no hemoglobin detected, the meter automatically assumes that the test element is a control element. This methodology is in essence binary, and is limited to the distinction between xe2x80x9cBloodxe2x80x9d and xe2x80x9cNot Blood,xe2x80x9d and is therefore not satisfactory if there are more than two possibilities.
The difficulties monitoring devices have in properly distinguishing the type of test element inserted also carries over to distinguishing between insertion of a test strip having a sample applied thereon, i.e. a control test element or an analytical test element, and insertion of a standard reflectance strip. Again, conventional monitoring devices have the drawback of requiring an affirmative act from the user to signal that a non-analytical test is being performed by the monitoring device. It is accordingly an object of the invention to provide a method for automatically distinguishing between the type of test performed by the device based on the test element inserted by the user, without the need for any affirmative act by the user.
In accordance with the invention, a method for automatically selecting test types in an analytical meter system is described, the method comprising the steps of:
providing a test element, said test element belonging to one of a plurality of test element types;
inserting said test element into an analytical meter system;
measuring a first optical property of the test element;
measuring a second optical property of the test element;
distinguishing said test element by identifying a predetermined relationship between said first and second optical properties;
selecting a test type based at least in part upon the results of said distinguishing step.
Also described is a meter system for performing one of a plurality of test types on a test element, where the test element is inserted into the meter system and belongs to one of a plurality of test element types, the meter system comprising:
a first light emitting diode selectively discharging light at a first wavelength;
a second light emitting diode selectively discharging light at a second wavelength;
at least one light detector for measuring light emitted from the first and second light emitting diodes and reflected from a test element; and
a processor for distinguishing said test element by identifying a predetermined relationship between first and second optical properties, and further for selecting a test type based at least in part upon the results of said distinguishing.
Additional objects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention will be realized and attained by means of the elements and combinations particularly pointed out in the appended claims.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention, as claimed.